The NFIB, a group representing small business owners, compiled the index from a survey of its members. It found that owners’ expectations for sales and profits fell last month. Plans to hire more workers also fell.

The drop in the index to a reading of 92.5 from February’s 94.3 follows six months of gains. The index was at a low of 81 in April 2009, just after the stock market hit bottom during the recession.

NFIB Chief Economist William Dunkelberg said the rising price of gasoline is making owners more pessimistic.

“More people are complaining about inflation, which usually means energy prices,” he said.

Gas prices fell by about a penny over the weekend to a national average of nearly $3.93 a gallon, according to auto club AAA, Wright Express and Oil Price Information Service. The average price of gasoline could surpass $4 per gallon nationwide as early as this week.

The NFIB also noted that uncertainty about Europe’s financial crisis remained, and that uncertainty about health care increased as the Supreme Court heard arguments seeking to have the law that overhauled health care declared unconstitutional.